1. Field of the Invention
The present invention relates to a method for producing a duplicate hologram recording medium, an apparatus for producing a duplication master, an apparatus for producing a duplicate hologram recording medium, and a duplication master.
2. Description of the Related Art
In recent years, a holographic memory has been attracting attention as a data storage device that can achieve high recording density and enables recording and reproduction of recording data at high transfer rate. In a holographic memory, by making use of also the thickness direction of a recording medium, at the time of recording, the interference fringes between a reference beam and a signal beam are formed in a hologram recording medium as holograms on the basis of page data corresponding to recording data with two-dimensional information as one page unit, thereby performing recording at once in a three-dimensional manner. Further, at the time of reproduction, diffracted beams generated upon radiating reference beams to the holograms thus formed are obtained to thereby reproduce recording data (see Japanese Unexamined Patent Application Publication No. 2004-226821, and Nikkei Electronics, Jan. 17, 2005, pp. 106-114).
On the other hand, data storage devices based on the CD (Compact Disc) format or the DVD (Digital Versatile Disc) format are currently in widespread use. In these techniques, not only recording media that permit additional writing or rewriting to the media but also ROM media (Read Only Media) that can be mass-duplicated for distribution, such as a CD-ROM and a DVD-ROM, are being widely used. In a CD-ROM or a DVD-ROM, there is adopted a method in which an original disk for duplication, that is, a master disk is prepared, or a mother disk is further prepared from the master disk, and with the master disk or mother disk as the original disk, resin is poured into a mold made from this original disk to perform molding, thereby mass-producing CD-ROMs or DVD-ROMs as the replicas of the original disk.
For hologram recording media as well, like the CD-ROMs or DVD-ROMs described above, mass duplication of hologram recording media with holograms of the same shape formed therein has been considered. Such a technique is disclosed in International Publication WO 2005/038789A1. International Publication WO 2005/038789A1 discloses a method of recording optical information into an optical information recording medium that serves as the original for mass duplication of a hologram recording medium on which holograms have been recorded, a method of recording optical information into another optical recording information medium using such an optical recording information medium serving as the original. The key technical point for such a technique is how to enable high-speed recording to a large quantity of duplicate optical recording information media.
According to International Publication WO 2005/038789A1, in view of the above-mentioned point, the following method is employed as the method of recording optical information into an optical information recording medium that serves as an original for duplication. That is, a virtual information beam including an information beam carrying information and a recording reference beam is generated, and the virtual information beam and a virtual recording reference beam are radiated to the optical information recording medium. Further, as for the method of recording optical information into a duplicate optical information recording medium, there is described a technique in which a virtual reconstruction reference beam is radiated to an optical information recording medium that serves as an original, and a virtual information beam generated from the optical information recording medium serving as an original is radiated to an optical information recording medium, and there is disclosed a technique in which virtual information beams are radiated to an optical information recording medium at once using a large-aperture objective lens.
Further, in F. Mok “Holographic Read-Only Memory” in Holographic Data Storage, H. J. Coufal, D. Psaltis, and G. Sincerbox, eds., (Springer-Verlag, New York, 2000), there is disclosed a technique of duplicating a replica by arranging a master (original disk) and a replica (duplicate disk) adjacent to each other, and making a reconstruction reference beam and a replica-transfer reference beam common.